Photo: Tony Avelar-AP Photo The San Francisco 49ers went through a lot in the offseason, but did a pretty good job of addressing several key areas with their picks in the NFL Draft. They lost several players to retirement from the defensive side of…

Photo: Matt Slocum-Associated Press While many of the faces in this picture are gone, the 49ers are using the 2015 NFL Draft to replenish a much-depleted defense that has seen several players retire. Gone are the likes of Willis and Borland, but in come…